Carburettor containing porous material e. g. foamed plastic

ABSTRACT

A carburettor, particularly for use with a petrol driven internal combustion engine, having a porous member, means for supplying petrol to it via a metering orifice from a constant level reservoir, means whereby the vacuum produced by the engine draws air through the porous member to produce a petrol/air mixture and a shutter located close to the downstream face of the porous member and adapted to move across the said face so as to shield progressively a variable area thereof and thus concentrate the air flow through certain zones of the porous member. The carburettor should be cheaper to manufacture than conventional carburettors, with which its performance compares favorably.

United States Patent 1151 3,695,593 Postlethwaite 1 Oct. 3, 1972 [54] CARBURETTOR CONTAINING 3,336,734 8/1967 Schultz ..261/96 POROUS MATERIAL E. G. FOAMED 765,108 7/1904 Soeder ..261/96 PLASTIC FOREIGN PATENTS OR APPLICATIONS [72] Inventor: Harvey Ernest Postlethwaite, Runcom, England 12,186 4/1915 Great Bntaln ..261/96 14,026 6/1914 Great Britain ..261/105 [731 Asslgmfi f f Chemml lndusmes 118,430 8/1918 Great Britain. ..261/96 140mm", England 565,153 10/1944 Great Britain ..261/99 [22] Filed: Sept. 10, 1970 R Ml Primary Examiner-Tim 1 es [211 App! 71l30 Attorney-Cushman, Darby & Cushman [30] Foreign Application Priority Data [57] ABSTRACT Sept. 15, 1969 Great Britain ..45,290/69 A carburettor, particularly for use with a petrol driven internal combustion engine, having a porous member, [52] US. Cl ..261/96, 261/99 means for supplying petrol to it via, a metering orifice [51] Int. CI ..F02m from a constant level reservoir, means whereby the Field 0f Search 99, 97, 44 R, vacuum produced by the engine draws air through the 261/65 porous member to produce a petrol/air mixture and a shutter located close to the downstream face of the [56] References C'ted porous member and adapted to move across the said UNITED STATES PATENTS face so as to shield progressively a variable area thereof and thus concentrate the air flow through cer- McBean et al tain zones of the porous member The carburettor 1,232,699 7/ 1917 Lindenberg should be cheaper to manufacture than conventional 3,151,188 9/1964 weatherston ct X carburettors, with which its performance compares 3,572,656 3/1971 Oshima ..261/65 f bl 450,091 4/1891 Woolley ..261/97 3,309,070 3/ 1967 Wilson ..261/69 R 13 Claims, 7 Drawing Figures ll/l/l Ill/l Aflornvy! 7 Q CARBURET'IOR CONTAINING POROUS MATERIAL E. G. FOAMED PLASTIC This invention relates to carburetors and especially to carburettors intended for use with internal combustion engines.

The carburetors most commonly fitted to petroldriven internal combustion engines are of multi-component construction comprising a die-cast body of complex shape into which a series of carefully machined metering jets are fitted, the carburetor usually being provided with ancillary devices whereby the contribution of each jet to the total fuel supply may be constantly regulated to produce the air/petrol mixture required under the prevailing running conditions of the engine.

Carburetors have also been proposed in which an absorbent material is dipped into a reservoir of petrol so that it impregnates the absorbent material by capillary attraction, the petrol/air mixture being obtained by directing a stream of air through the impregnated material. These are commonly termed wick-type carburetors. It has also been proposed to soak a packed particulate mass with petrol and direct air through it to produce a petrol/air mixture. Carburetors have also been proposed in which a porous member is impregnated with a liquid fuel, and a stream of air 'directed across a surface of the porous member to produce a petrol/air mixture. These are commonly termed surface type.carburetors.

However, carburetors of the last-mentioned types, although obviating the need for a series of carefully machined jets, suffer from the particular disadvantages that it is difficult to provide adequate control of the petrol/air ratio of the resultant mixture, and that they do not respond rapidly to sudden variations in throttle setting.

We have now devised a carburetor whichemploys a porous member as a vaporizing or atomizing means in which the aforementioned disadvantages are obviated or at least alleviated.

According to the present invention, a carburetor U suitable for use with an internal combustion engine comprises a three-dimensional porous member, means for supplying a vaporizable liquid to the pores of said member at a controllable rate, means wherebya stream of gas may be directed through the porous member from one to another of its outer surfaces, thereby producing a gas/vapor mixture (as hereinafter defined), a shutter located downstream of the porous member and means for causing relative movement between the porous member and shutter in a plane substantially parallel to the downstream outer surface of the porous member to shield progressively a variable area of said outer surface, the shutter being close enough to said outer surface for its interaction with the gas stream to concentrate the gas flow through the porous member into a zone or zones extending upstream from the unshielded area, and the said liquid supply means being arranged so that liquid is supplied to that part or those parts of the porous member which is or are first shielded during said progressive shielding.

We intend the term gas/vapor mixture to include mixtures in which the vaporizable liquid exists as a vapor, as atomized droplets or as a mixture of said forms.

Preferably the means for directing a stream of gas through the porous member takes the form of a elongate, tube-like passage in which the porous member is locatable so that all or substantially all of the gas stream may be directed through it, usually by means of the vacuum generated by the engine to which the carburetor is attached. it is further preferred that the porous member should fill a section of the bore of the passage completely so that all air passing; through the chamber must do so by way of the porous member.

For the purposes of this specification, the term shutter is intended to include any solid body which will accommodate the required relative movement and deflect or arrest the gas stream passing through the porous member. The shutter may comprise one or more generally laminar members which are adapted to slide or rotate in the plane of movement so as to present to the appropriate face of the porous member a shield of variable area. The shutter preferably takes the form of a slide having at least one flat face, and arranged so that its leading edge will traverse the bore of the tube-like passage from one edge to the other to provide the said progressive shielding. Alternatively an iris diaphragm or cam-like rotatable slide may be used. It is alsopossible to provide the shutter with graded apertures which may be moved progressively into and out of the gas flow.

The ideal axial distance of the shutter from the shielding face of the porous member (i.e., measured in the overall direction of gas flow) will depend on various design parameters of the carburetor and the conditions under which it is to be used; but may be readily determined by experiment. As a general rule, it is preferred that the distance between the shutter and the said shielded face should be no more than one quarter of the maximum dimension of the shielded face. However it is preferable to locate the shutter as close as mechanically convenient to the shielded face to obtain closest control of the aforementioned concentration of gas flow.

Although the factors governing the relationship between the location of the shutter and the performance of carburetors according to our invention are complex and not fully understood, it will be appreciated that, as the distance between shutter and porous member is increased, the shielding movement will tend to cause variations in the rate of gas flow through the full area of the shielded face rather than to concentrate it in the unshielded area or areas.

By three-dimensional porous member we mean a porous structure in which the pores extend in three dimensions, so that a gas stream passing through the member must traverse successively two or more pores in passing from one outer surface of the member to the other. i

The porous member may be constructed from any porous material having an open-cell structure which is inert to petrol, or whatever vaporizable liquid is to be used in the device, and is physically capable of withstanding the passage of a gas stream through it. By open cell structure we mean having a multiplicity of cells and/or passageways connecting one with another and with the surrounding atmosphere to allow passage of gas through the said structure.

It is possible to use naturally occuring porous materials, for example, natural sponge or pumice; but the use of artificially produced porous materials is much preferred, as it is possible to control the porosity of such materials to a much greater extent than is possible with naturally occuring materials.

Examples of artificially produced porous materials include artificial foams, such as those produced by foaming a liquid or molten material and causing it to solidify in its foamed condition. Examples of such materials include the so-called polymeric foams, e,g., of the polyurethanes, and metal or metallized foams. The foams may be rigid or flexible provided that they possess sufficient strength to withstand the stresses imposed by the gas flow, and are substantially unaffected by the Vaporizable liquid.

Additional strength and/or rigidity may be achieved by the incorporation of reinforcing members such as metal wires or meshes into the porous member or by the location of such reinforcements against the downstream face of the porous member. Metal or metallized foams possess the additional property of thermal and/or electrical conductivity.

The use of foamed materials as the material of construction of the porous member may provide ancillary advantages in that construction of carburetors according to our invention may be accomplished by in situ formation of the porous member, and in that some control may be exercised over the size and alignment of the pores by choice and control of foaming conditions, etc.

The porous member may alternatively comprise a packed mass of an inert particulate or fibrous material, for example, glass beads, powdered alumina, glass or metal wool or polymeric fibrous material. It is usual, especially in the case of particulate materials, to confine the packed mass by means of, for example, gauze screens. The particulate or fibrous material may also be bonded into a self-supporting porous structure, for example, by sintering or by the use of adhesives. For example, when polymeric fibers are used it is possible to use a fiber having an outer skin of a low-melting material so that moderate heating of the packed mass causes the fibers to bond together at their intersection points without melting or even softening of the bulk of the material.

When a packed mass of material is used to form the porous member, it has been found desirable to employ random distribution of the particles or fibers to avoid, or at least minimize, the incidence of channelling, that is, the undesired formation of channels or passageways having considerably less resistance to gas flow than the bulk of the material.

Porous materials having a range of porosities may be used in carburetors according to our invention, the ideal porosity for a particular carburetor being linked to several interdependent factors which include the cross-sectional area and thickness of the porous member, and the operating conditions under which the carburetor is to be used. However, the most important consideration is the overall resistance of the porous member to gas flow, as discussed in more detail below.

Vaporizable liquid may be conveniently supplied to the porous member at a controlled rate by arranging for the liquid to pass to the porous member by way of a metering orifice, that is, an orifice of variable or predetermined geometry. One convenient form' of metering orifice consists of a constriction situated in the supply pipe to the porous member. However, the orifice may take other forms, for example, the multiplicity of orifices presented b a porous material may be made to function in this way. Thus it may be possible to use part of the porous member of the carburetor for this purpose. The resistance to gas flow through the porous member is preferably sufficient to provide a pressure drop at the said metering orifice which will result in the required flow of liquid to the porous member. However, in carburetors according to our invention which are intended to be used with a petrol-driven internal combustion engine, the porosity and geometry of the porous member are chosen so as to avoid undue resistance to the airflow required by the engine at high speeds.

Preferably the Vaporizable liquid is supplied by way of a constant level reservoir such as a float chamber, as used in conventional carburetors. Further, it is preferred that the level of liquid in the reservoir is maintained at or slightly below the point at which the liquid is introduced into the porous member when in its normalv working position, so that liquid flow does not occur under gravity, but'is induced by the aforementioned pressure drop generated by the flow of gas through the porous member.

It will be appreciated that there will be a certain relationship between the pressure drop at the metering orifice and the gas flow through the porous member, and that another relationship will exist between the said pressure drop and the flow of liquid through the metering orifice. Thus, by careful design of the orifice, it is possible to match these two relationships in such a way that the vapor to gas ratio of the mixture produced' either remains substantially constant or varies in some desired manner with changes in gas flow.

When conditions are chosen so that the vapor/gas ratio is substantially constant, it has been found that the position of the shutter has a slight effect upon the relationship between gas flow through the porous member and the pressure drop induced at the orifice and hence the flow of liquid therein. For example, the effect of opening the slide is to cause a slight increase in the pressure drop induced at the orifice for a given gas flow through the member, giving rise to a corresponding slight increase in the vapor/ gas ratio.

When carburetors according to our invention are used with a petrol engine, this effect may be used to give rise to a desirable slight increase in mixture strength upon prolonged acceleration under load.

Although it is essential that Vaporizable liquid is sup plied to that part of the porous member which is first shielded, it is possible and may sometimes be desirable to provide an ancillary supply to another part or parts of the member. It may also be advantageous to segregate a small part of the member from the rest and to provide that part with its own liquid supply, for example to improved slow-running characteristics when our carburetors are applied to petrol engines, as described in more detail later.

The term carburetor is used in this specification in the generic sense, that is, to denote a device for producing a controlled mixture of vapor and gas from a Vaporizable liquid and a gas; but the invention is especially directed to carburetors intended for use with petrol-driven internal combustion engines. For the sake of simplicity, the invention is hereinafter explained and illustrated by reference only to such carburetors, the term petrol being used instead of vaporizable liquid and the term "air being used instead of gas; but it is not intended that this should limit the application of our invention.

Carburetors according to our invention which are intended for use with petrol-driven internal combustion engines preferably comprise a hollow body provided with a tube-like passage extending therethrough in which a porous member is locatable so as to fill or substantially fill a section of the bore of said passage, and inlet and outlet ports connecting with respective ends of the passage, the outlet port being adapted for connection to the inlet manifold of an internal combustion engine to enable air to be drawn through the porous member by means of the vacuum produced by opera tion of the engine. The shutter, which preferably takes the form of a flat-faced slide, the flat face of which is arranged close to the downstream face of the porous member, is provided with suitable bearing means to enable it to traverse the bore of the passage so as to shield a variable area of the said face of the porous member. A form of slide in which the bearing friction is appreciably reduced comprises a generally cylindrical I member having a longitudinal segment removed over part of its length to form a flat face over that part. Such a slide is readily mountable as a sliding fit in a cylindrical cavity to give a low resistance to sliding coupled with good rigidity to withstand the effects of air pressure on the upstream face of the slide.

In order that the invention may be more fully understood, two embodiments will now be described, by way of example only, with reference to theaccompanying drawings of which FIG. 1 is a sectional elevation of a side-draught carburetor according to our invention;

FIG. 2 is an end elevation of the same carburetor, looking inthe direction of arrows Il-ll;

FIG. 3 is a sectional elevation of a down-draught carburetor according to our invention on the line III--Ill shown in FIG. 4;

FIG. 4 is another sectional elevation of the carburetorillustrated in FIG. 3 on the LineIV-IV; and

FIG. 5 is a plan view of the carburetonillustrated in FIGS. 3 and 4.

Referring to FIGS. 1 and 2, cylindrical *tube 10 of poly (4-methyl-pentene-l) having a 1 9% inch bore was provided with aporous member 11 in the form of a block of foamed, open-cell, flexible polyurethane, cut to fill a section of tube 10 and bonded to the walls with epoxy resin. Tube .10 was further provided with a fuel supply pipe 12 and a shutter in the form of slide plate 13 of poly(4-methylpentene-l) sheet, capableof sliding (as indicated inbroken lines in FIG. I) in a parallelsided slot 14 in tube 10. Thelower edge of slide plate 13 was curved, as shown in FIG. 2, toena'ble it to mate against the inner wall of tube 10 when initsfully inserted position. In this prototype carburetor, slide plate 13 was arranged to be aclose fit in slot 14, a reasonably gas-tight seal being provided by the natural resilience of the material of tube 10. However, it will. be appreciated that ancillary sealing means could readily be provided if necessary.

In use, the end of tube 10 nearest to slide plate 13 was connected to the inlet manifold of a four-stroke 250 cc petrol engine, and petrol was supplied to feed pipe 12 via a float chamber and a metering orifice (not shown) consisting of a variable orifice needle valve. Slide plate 13 was set in an intennediate open position and the engine started. The setting of the metering orifice was then adjusted until it provied possible to adjust the position of slide 13 to cause the engine to tickover steadily. Rapid movement of the slidel3 out of tube 11 was then accompanied by a rapid and controllable response in the speed of the engine.

Without prejudice to the invention, it is thought that this rapid response is due to a temporary enrichment of the petrol/air mixture caused by the sudden exposure of air flow of a previously stagnant zone of the porous member through which petrol has been permeating. This temporary enrichment may be desirable in certain circumstances.

Another desirable feature of carburetors according to our invention is the high degree of mixing promoted by the turbulence generated by air flow through the porous member. This appears to. give rise to good cold starting with little or no choking and, without prejudice to the invention, it is believed that this could also permit the successful use of a leaner mixture, which could confer the advantages of lower fuel consumption and possibly a decrease of toxic emission from the engine.

Referring now to FIGS. 3, 4 and 5, metal body 14 comprises a rectangular block of metal provided with two generally cylindrical intersecting bores ;l5, 16.

Here 15 runs longitudinally through a major portion of the body 14, while bore 16 runs; transversely through the body at the inner extremity of bore 15, with which it intersects. Bore 16 is provided at one end with coaxial metal sleeves 17, 18 which fit one within the other and co-operate to define annularcavity'19 which connects with diametrically opposed orifices 20, 21 machined in sleeve 18. Annular cavity 19 connects with cylindrical aperture 22 which is connectable to a float chamber (not shown) the level of petrol in which is maintained level with or below the outlets of orifices 20, 21. Porous members 23, 24 consist of crimped nylon monofilament randomly packed into the space defined. by the inner surface of sleeve 18, the packing density being greaterin member 24. Porous members 23, 24 are separated by curved metal strip 25, orifices 20 and 21 opening into members v24 and 23 respectively. Slide 26 consists of a cylindrical block of metal from which a longitudinal segment has been machined to define flat face 27 which extends over part of its length. Longitudinal cylindrical cavity 28 extends over a major portion of the length of slide 26. Slide 26 is a sliding fit within bore 16 of body 14, so that flat face 27 is slidable over the lower faces of porous members 23, 24. Slide 26 is urged resilientlyinto its fully-inserted position by the reaction of compression spring 29 against end plate The carburetor illustrated in FIGS. 3, 4 and 5 operates in similar fashion to that illustrated in FIGS. 1 and 2, in that, when slide 26 is withdrawn to expose porous members 23 and 24, air is drawn through them (as indicated by arrows) by the vacuum generated by rotation of the engine, the resulting pressure drop causing petrol to be drawn into the porous members from orifices and 21.

In general running, porous member 23 behaves in the same manner as described for porous member 11 in FIG. I; but it is arranged that when slide 26 moves to a nearly closed position so that only porous member 24 is exposed to air flow, i.e., when the engine is ticking over, petrol is drawn almost exclusively from porous member 24 via orifice 20. In order to facilitate operation in this way, it may be desirable to grade the orifices which supply the respective zones of the porous member. For example, in the second embodiment illustrated, orifices 20 and 21 were of 13 and 60 thousandths of an inch diameter, respectively. The previously mentioned different packing densities of members 23 and 24 was also designed to facilitate obtaining the desired balance between running and tick over conditions. Measurements showed that the variation of petrol/air ratio was maintained between l2/l and 14/ I over the whole range of slide positions.

The carburetor illustrated in FIGS. 3, 4 and 5 was fitted to the engine of a standard, production model 1,600 cc estate car. The vehicle ran satisfactorily in this way for several thousand miles, and with a performance and fuel consumption comparable to that obtained using the conventional carburetor supplied with the vehicle. This is illustrated graphically in FIGS. 6 and 7. In FIG. 6, which relates to fuel consumption, the results for the conventional carburetor are shown by the broken line and those for a carburetor according to our invention by the solid line. It will be noted that when using our carburetor, fuel consumption was improved over much of the range. FIG. 7 relates to performance as indicated by acceleration through the gears from O to 70 mph. (Graphs A), and in second gear from 20 to 70 mph. (Graph B). In each case the broken line relates to the conventional carburetor and the solid line to our carburetor.

Although the second embodiment of our invention was constructed largely of metal, it will be appreciated that other materials, e.g., plastics, could be readily employed instead. It is considered, without prejudice, that carburetors according to our invention might be produced more cheaply and simply than many conventional carburetors, despite the fact that their performance is likely to be at least comparable.

Although our carburetors have been described hitherto with in situ porous members, it will be readily appreciated that, by appropriate design of carburetor body, the porous member may be formed as an interchangeable element, or cartridge, which is locatable, for example, in the tube-like passage. This enables the porous member to be easily exchanged or removed for cleaning should it become blocked by foreign matter carried into it from the petrol or air passing through it.

What we claim is:

l. A carburetor, suitable for use with a petrol-driven internal combustion engine, which consists essentially of a carburetor body having a tube-like passage therein,

a three-dimensional porous member located in said passage, said body including means for connecting the same to the inlet manifold of an internal combustion engine so that the vacuum caused by rotation of the engine draws at least substantially all of the air necessary for operation of said engine through the porous member, means for supplying petrol to the pores of said member at a controllable ratio so that passage of air through the member produces an air/petrol vapor mixture, a shutter located downstream of the porous member and means for causing relative movement between the porous member and shutter in a plane substantially parallel to the downstream outer surface of the porous member to shield progressively a variable area of said outer surface, the shutter being close enough to said outer surface for its interaction with the air stream to concentrate the air flow through the porous member into a zone or zones extending upstream from the unshielded area, and the said petrol supply means being arranged so that petrol is supplied to that part of those parts of the porous member which is or are first shielded during said progressive shielding, the said porous member being so arranged that all or substantially all of the air stream through the carburetor passes through the porous member.

2. A carburetor as claimed in claim 1 in which the porous member fills a section of the bore of the said passage.

3. A carburetor as claimed in claim 1 in which the shutter takes the form of a slide having at least one fiat face, arranged so that its leading edge may be caused to traverse the bore of the passage from one edge to the other to provide the said progressive shielding.

4. A carburetor as claimed in claim 1 in which the axial distance between the shutter and the shielded face of the porous. member is not more than one quarter of the maximum dimension of the shielded face.

5. A carburetor as claimed in claim 4 in which the shutter is located as close to the said shielded face as is mechanically convenient.

6. A carburetor as claimed in claim 1 in which an open cell foamed material; formed by foaming a liquid or molten material and causing it to solidify in the foamed condition, is used as the porous member.

7. A carburetor as claimed in claim 6 in which the material is selected from polymeric, metal and metallized foamed materials.

8. A carburetor as claimed in claim 1 in which the porous member comprises a packed mass of inert fibrous, filamentary or particulate material.

9. A carburetor as claimed in claim 1 in which the petrol supply means includes a metering orifice through which petrol passes to the porous member.

10. A carburetor as claimed in claim 1 which is provided with means whereby the petrol may be supplied to the porous member from a constant level reservoir, the level of which is maintainable at or slightly below the point at which petrol is introduced into the porous member when in its normal working position.

11. A carburetor as claimed in claim 1 in which a minor portion of the porous member is segregated from the rest and provided with its own petrol supply means, said minor portion being located in that part of the porous member which is last shielded during the said progressive shielding. 

2. A carburetor as claimed in claim 1 in which the porous member fills a section of the bore of the said passage.
 3. A carburetor as claimed in claim 1 in which the shutter takes the form of a slide having at least one flat face, arranged so that its leading edge may be caused to traverse the bore of the passage from one edge to the other to provide the said progressive shielding.
 4. A carburetor as claimed in claim 1 in which the axial distance between the shutter and the shielded face of the porous member is not more than one quarter of the maximum dimension of the shielded face.
 5. A carburetor as claimed in claim 4 in which the shutter is located as close to the said shielded face as is mechanically convenient.
 6. A carburetor as claimed in claim 1 in which an open cell foamed material; formed by foaming a liquid or molten material and causing it to solidify in the foamed condition, is used as the porous member.
 7. A carburetor as claimed in claim 6 in which the material is selected from polymeric, metal and metallized foamed materials.
 8. A carburetor as claimed in claim 1 in which the porous member comprises a packed mass of inert fibrous, filamentary or particulate material.
 9. A carburetor as claimed in claim 1 in which the petrol supply means includes a metering orifice through which petrol passes to the porous member.
 10. A carburetor as claimed in claim 1 which is provided with means whereby the petrol may be supplied to the porous member from a constant level reservoir, the level of which is maintainable at or slightly below the point at which petrol is introduced into the porous member when in its normal working position.
 11. A carburetor as claimed in claim 1 in which a minor portion of the porous member is segregated from the rest and provided with its own petrol supply means, said minor portion being located in that part of the porous member which is last shielded during the said progressive shielding.
 12. A carburetor as claimed in claim 11 in which the minor portion of the porous member has a lower porosity than that of the rest of the porous member.
 13. In combination with a petrol-driven internal combustion engine including an inlet manifold, a carburetor as defined in claim
 1. 